SDS-induced hexameric oligomerization of myotoxin-II from Bothrops asper assessed by sedimentation velocity and nuclear magnetic resonance.

We report the solution behavior, oligomerization state, and structural details of myotoxin-II purified from the venom of Bothrops asper in the presence and absence of sodium dodecyl sulfate (SDS) and multiple lipids, as examined by analytical ultracentrifugation and nuclear magnetic resonance. Molecular functional and structural details of the myotoxic mechanism of group II Lys-49 phospholipase A2 homologues have been only partially elucidated so far, and conflicting observations have been reported in the literature regarding the monomeric vs. oligomeric state of these toxins in solution. We observed the formation of a stable and discrete, hexameric form of myotoxin-II, but only in the presence of small amounts of SDS. In SDS-free medium, myotoxin-II was insensitive to mass action and remained monomeric at all concentrations examined (up to 3 mg/ml, 218.2 µM). At SDS concentrations above the critical micelle concentration, only dimers and trimers were observed, and at intermediate SDS concentrations, aggregates larger than hexamers were observed. We found that the amount of SDS required to form a stable hexamer varies with protein concentration, suggesting the need for a precise stoichiometry of free SDS molecules. The discovery of a stable hexameric species in the presence of a phospholipid mimetic suggests a possible physiological role for this oligomeric form, and may shed light on the poorly understood membrane-disrupting mechanism of this myotoxic protein class.

Effects of feeding a pine-based biochar to beef cattle on subsequent manure nutrients, organic matter composition and greenhouse gas emissions.

Biochar in ruminant diets is being assessed as a method for simultaneously improving animal production and reducing enteric CH4 emissions, but little is known about subsequent biochar-manure interactions post-excretion. We examined chemical properties, greenhouse gas (GHG) emissions and organic matter (OM) composition during farm scale stockpiling (SP) or composting (CP) of manure from cattle that either received a pine-based biochar in their diet (BM) or did not (RM). Manure piles were monitored hourly for temperature and weekly for top surface CO2, N2O and CH4 fluxes over 90 d in a semiarid location near Lethbridge, AB, Canada. Results indicate that cumulative CO2, N2O and CH4 emissions were not affected by biochar, implying that BM was as labile as RM. The pH, total C (TC), NO3-N and Olsen P were also not influenced by biochar, although it was observed that NH4-N and OM extractability were both 13% lower in BM than RM. Solid-state 13C nuclear magnetic resonance (NMR) showed that biochar increased stockpile/compost aromaticity, yet it did not alter the bulk C speciation of manure OM. Further analysis by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) revealed that dissolved OM was enriched by strongly reduced chemical constituents, with BM providing more humic-like OM precursors than RM. Inclusion of a pine-based biochar in cattle diets to generate BM is consistent with current trends in the circular economy, "closing the loop" in agricultural supply chains by returning C-rich organic amendments to croplands. Stockpiling/composting the resulting BM, however, may not provide a clear advantage over directly mixing low levels of biochar with manure. Further research is required to validate BM as a tool to reduce the C footprint of livestock waste management.

Chalcogen versus Dative Bonding in [SF3]+ Lewis Acid-Base Adducts: [SF3(NCCH3)2]+, [SF3(NC5H5)2]+, and [SF3(phen)]+ (phen = 1,10-phenanthroline).

The Lewis-acid behavior of [SF3][MF6] (M = Sb, As) salts toward mono- and bidentate nitrogen bases was explored. Reactions of [SF3][MF6] with excesses of CH3CN and C5H5N yielded [SF3(L)2]+ (L = CH3CN, C5H5N) salts, whereas the reaction of [SF3][SbF6] with equimolar 1,10-phenanthroline (phen) in CH3CN afforded [SF3(phen)][SbF6]·2CH3CN. Salts of these cations were characterized by low-temperature X-ray crystallography and Raman spectroscopy in the solid state as well as by 19F NMR spectroscopy in solution. In the solid state, the geometries of [SF3(NC5H5)2]+ and [SF3(phen)]+ are square pyramids with negligible cation-anion contacts, whereas the coordination of CH3CN and [SbF6]- to [SF3]+ in [SF3(NCCH3)2][SbF6] results in a distorted octahedral coordination sphere with a minimal perturbation of the trigonal-pyramidal SF3 moiety. 19F NMR spectroscopy revealed that [SF3(L)2]+ is fluxional in excess L at -30 °C, whereas [SF3(phen)]+ is rigid in CH2Cl2 at -40 °C. Density functional theory (DFT-B3LYP) calculations suggest that the S-N bonds in [SF3(NC5H5)2]+ and [SF3(phen)]+ possess substantial covalent character and result in a regular AX5E VSEPR geometry, whereas those in [SF3(NCCH3)2]+ are best described as S···N chalcogen-bonding interactions via σ-holes on [SF3]+, which is consistent with the crystallographic data.

Molecular speciation and aromaticity of biochar-manure: Insights from elemental, stable isotope and solid-state DPMAS 13C NMR analyses.

The use of biochar (BC) in feedlot cattle diets has recently been explored as an approach to simultaneously improving animal production and reducing enteric methane (CH4) emissions. This study examines the impact of BC on manure properties and whether BC affects manure composition and carbon (C) and nitrogen (N) outputs from feedlot steers offered a barley-based diet with BC at 0.0, 0.5, 1.0 and 2.0% (BC0, BC0.5, BC1 and BC2) of diet dry matter. Manure was sampled three times over a 235 day feeding trial conducted in southern Alberta, Canada. Results showed that BC2 increased total C and the C/N ratio by 5.7 and 6.6% relative to BC0, respectively (P < 0.05), while total N exhibited a quadratic response from BC0 to BC2 (P = 0.005). Manure 15δN signatures, ranging from +3.83 to +7.34‰, were not affected (P > 0.05) by BC treatment. DPMAS 13C NMR revealed similar structural features among BC0 and BC2; indigestible BC had a minor impact on the bulk-C speciation of manure organic matter (OM). Compositional changes were limited to the aromatic-C region of the 13C NMR spectra. Fused-ring domains, mainly pyrogenic-C, were increased by 1.56-fold at BC2 relative to BC0. Overall, results demonstrated that BC stabilizes recalcitrant-C in manure OM, potentially sequestering soil-C when applied to croplands. This approach provides an added value to its use in ruminant diets, mainly from a nutrient cycling perspective. However, whole-farm studies are further required to validate the incorporation of BC into beef production systems.

Reactions of Molybdenum and Tungsten Oxide Tetrafluoride with Sulfur(IV) Lewis Bases: Structure and Bonding in [WOF4]4, MOF4(OSO), and [SF3][M2O2F9] (M = Mo, W).

The structure of [WOF4]4 has been reinvestigated by low-temperature X-ray crystallography and DFT (MN15/def2-SVPD) studies. Whereas the W4F4 ring of the tetramer is planar and disordered in the solid state, the optimized gas-phase geometry prefers a disphenoidally puckered W4F4 ring and demonstrates asymmetric fluorine bridging. Dissolution of MOF4 (M = Mo, W) in SO2 and SF4 results in the formation of MOF4(OSO) and [SF3][M2O2F9], respectively. Both SO2 adducts and [SF3][Mo2O2F9] have been characterized by X-ray crystallography. The crystal structure of [SF3][Mo2O2F9] reveals dimerization of the ion pair that results in a rare heptacoordinate sulfur center. Optimization of the {[SF3][M2O2F9]}2 dimers in the gas phase, however, results in the elongation of one contact such that the sulfur centers are effectively hexacoordinate. Meanwhile, the crystal structure of [SF3][W2O2F9]·HF instead demonstrates hexacoordinate sulfur centers and a highly unusual coordination to [SF3]+ from [W2O2F9]- through an oxido ligand. While [SF3][W2O2F9] does not decompose at ambient temperature, MOF4(OSO) and [SF3][Mo2O2F9] are unstable toward evolution of SO2 or SF4. Computational studies reveal that the monomerization of [WOF4]4 in the gas phase at 25 °C is thermodynamically unfavorable using SO2, but favorable using SF4, consistent with the relative thermal stabilities of WOF4(OSO) and [SF3][W2O2F9].

Stabilisation of [WF5 ]+ and WF5 by Pyridine: Facile Access to [WF5 (NC5 H5 )3 ]+ and WF5 (NC5 H5 )2.

The enhanced reactivity of [WF5 ]+ over WF6 has been exploited to access a neutral derivative of elusive WF5 . The reaction of WF6 (NC5 H5 )2 with [(CH3 )3 Si(NC5 H5 )][O3 SCF3 ] in CH2 Cl2 results in quantitative formation of trigonal-dodecahedral [WF5 (NC5 H5 )3 ]+ , which has been characterised as its [O3 SCF3 ]- salt by Raman spectroscopy in the solid state and variable-temperature NMR spectroscopy in solution. The salt is susceptible to slow decomposition in solution at ambient temperature via dissociation of a pyridyl ligand, and the resultant [WF5 (NC5 H5 )2 ]+ is reduced to WF5 (NC5 H5 )2 in the presence of excess C5 H5 N, as determined by 19 F NMR spectroscopy. Pentagonal-bipyramidal WF5 (NC5 H5 )2 was isolated and characterised by X-ray crystallography and Raman spectroscopy in the solid state, representing the first unambiguously characterised WF5 adduct, as well as the first heptacoordinate adduct of a transition-metal pentafluoride. DFT-B3LYP methods have been used to investigate the reduction of [WF5 (NC5 H5 )2 ]+ to WF5 (NC5 H5 )2 , supporting a two-electron reduction of WVI to WIV by nucleophilic attack and diprotonation of a pyridyl ligand in the presence of free C5 H5 N, followed by comproportionation to WV .

Influence of Long-term Application of Feedlot Manure Amendments on Water Repellency of a Clay Loam Soil.

Long-term application of feedlot manure to cropland may increase the quantity of soil organic carbon (C) and change its quality, which may influence soil water repellency. The objective was to determine the influence of feedlot manure type (stockpiled vs. composted), bedding material (straw [ST] vs. woodchips [WD]), and application rate (13, 39, or 77 Mg ha) on repellency of a clay loam soil after 17 annual applications. The repellency was determined on all 14 treatments using the water repellency index ( index), the water drop penetration time (WDPT) method, and molarity of ethanol (MED) test. The C composition of particulate organic matter in soil of five selected treatments after 16 annual applications was also determined using C nuclear magnetic resonance-direct polarization with magic-angle spinning (NMR-DPMAS). Manure type had no significant ( > 0.05) effect on index and WDPT, and MED classification was similar. Mean index and WDPT values were significantly greater and MED classification more hydrophobic for WD than ST. Application rate had no effect on the index, but WDPT was significantly greater and MED classification more hydrophobic with increasing application rate. Strong ( > 0.7) but nonsignificant positive correlations were found between index and WDPT versus hydrophobic (alkyl + aromatic) C, lignin at 74 ppm (O-alkyl), and unspecified aromatic compounds at 144 ppm. Specific aromatic compounds also contributed more to repellency than alkyl, O-alkyl, and carbonyl compounds. Overall, all three methods consistently showed that repellency was greater for WD- than ST-amended clay loam soil, but manure type had no effect.

Tetrabutylphosphonium Bromide Reduces Size and Polydispersity Index of Tat2:siRNA Nano-Complexes for Triticale RNAi.

Cell-penetrating peptides (CPPs) are short 8-30 amino-acid oligopeptides that act as effective transducers of macromolecular cargo, particularly nucleic acids. They have been implemented in delivering dsDNA, ssDNA, and dsRNA into animal and plant cells. CPPs and nucleic acids form nano-complexes that are often 100-300 nm in size but still effectively transit the cell membrane of animal cells, but are less effective with plant cells due to the plant cell wall. To overcome this obstacle, nano-complexes of the CPP Tat2 and various lengths of nucleic acid (21-mer siRNA duplex (dsRNA) to ~5.5 kb circular plasmid) were evaluated for size using dynamic light scattering (DLS), under conditions of increasing ionic strength (Ic) and addition of phase transfer catalyst salts (tetrabutylammonium bromide-TBAB and tetrabutylphosphonium bromide-TBPB) and sugars (maltose-mannitol solution). It was found that the combination of 21-mer siRNA:Tat2 complexes with TBPB produced small 10-20 nm diameter nano-complexes with a polydispersity index (PDI) of ~0.1. Furthermore, it was found that for each length of nucleic acid that a linear mathematical relationship existed between the theoretical volume of the nano-complex and the nucleic acid length. Next, nano-complex formulation was tested for its ability to carry small interfering RNA molecules into plant cells and to trigger silencing of phytoene desaturase (PDS) in Triticale leaves. RT-qPCR showed 75% suppression of PDS, demonstrating that TBPB acts as an adjuvant in effecting the entry and efficacy of siRNA in young Triticale plants.

Solvent and Water Mediated Structural Variations in Deoxynivalenol and Their Potential Implications on the Disruption of Ribosomal Function.

Fusarium head blight (FHB) is a disease of cereal crops caused by trichothecene producing Fusarium species. Trichothecenes, macrocylicic fungal metabolites composed of three fused rings (A-C) with one epoxide functionality, are a class of mycotoxins known to inhibit protein synthesis in eukaryotic ribosomes. These toxins accumulate in the kernels of infected plants rendering them unsuitable for human and animal consumption. Among the four classes of trichothecenes (A-D) A and B are associated with FHB, where the type B trichothecene deoxynivalenol (DON) is most relevant. While it is known that these toxins inhibit protein synthesis by disrupting peptidyl transferase activity, the exact mechanism of this inhibition is poorly understood. The three-dimensional structures and H-bonding behavior of DON were evaluated using one- and two-dimensional nuclear magnetic resonance (NMR) spectroscopy techniques. Comparisons of the NMR structure presented here with the recently reported crystal structure of DON bound in the yeast ribosome reveal insights into the possible toxicity mechanism of this compound. The work described herein identifies a water binding pocket in the core structure of DON, where the 3OH plays an important role in this interaction. These results provide preliminary insights into how substitution at C3 reduces trichothecene toxicity. Further investigations along these lines will provide opportunities to develop trichothecene remediation strategies based on the disruption of water binding interactions with 3OH.

The structure of trimethyltin fluoride.

The solid-state structure of (CH3)3SnF was reinvestigated by X-ray diffraction techniques as well as by multi-nuclear solid-state NMR spectroscopy. Trimethyltin fluoride crystallizes from hot ethanol in the orthorhombic space group Pnma at room temperature and changes to a low-temperature orthorhombic phase (space group: Cmcm) below -70 °C. In both modifications, trimethyltin fluoride adopts a linear chain structure with symmetric fluorine bridges, in contrast to previous reports. During its synthesis, (CH3)3SnF precipitates in another, poorly crystalline modification, as shown by powder X-ray diffraction. Solid-state MAS NMR experiments of both room-temperature phases of (CH3)3SnF (non-recrystallized and recrystallized) were carried out for the (1)H, (13)C, (19)F, and (119)Sn nuclei. The (119)Sn{(19)F, (1)H} and (19)F{(1)H} NMR spectra offer unambiguous determination for the (19)F and (119)Sn shielding tensors. The (119)Sn{(1)H} solid-state NMR spectra are in agreement with pentacoordination of Sn in this compound for the non-recrystallized and the recrystallized modifications. Based on the solid-state NMR results, the non-recrystallized modification of (CH3)3SnF also consists of linear, symmetrically fluorine-bridged chains, and differs from the recrystallized orthorhombic phase only in packing of the chains.

Investigation into the mechanism and microstructure of reaction intermediates in the two-phase synthesis of alkanethiol-capped silver nanoparticles.

To gain better control over the characteristics of the alkanethiol-capped silver nanoparticles (SNP) prepared by the two-phase method, the intermediate stage of this reaction and the structure of the precursor compound were investigated. Samples taken from the intermediate stage of the reaction were analyzed by NMR and vibrational spectroscopy both in solution and after solvent removal. The (1)H NMR chemical shifts of the complexes formed during the phase-transfer step were used to detect any structural changes that occur upon introduction of nonanethiol. Moreover, the presence of silver thiolate was monitored by comparing the FTIR and Raman spectra of silver nonanethiolate with the dried samples. Further insights into the microstructure of the intermediate compounds were sought by characterizing samples differing in molar ratios of tetraoctylammonium bromide (TOAB) to silver nitrate (AgNO3). (13)C solid-state NMR chemical shifts, (13)C relaxation times, and the DSC transitions of these samples revealed a dependence of their phase structure on the initial concentration of the reagents. At least two phases with distinct mobility and conformational ordering of their octyl chains were identified in the samples prepared with excess TOAB, which was associated with the presence of multiple anionic species. The observations regarding the composition of the phase-transfer product were further related to the quality of the resulting nanoparticles. It was demonstrated that a large excess of TOAB, which is commonly used in two-phase methods, can be avoided without compromising the size and dispersity of the silver nanoparticles produced. This modification to the synthetic procedure simplifies the purification of the product, mitigates the propensity of the nanoparticles for aggregation, and facilitates their redispersion.

Lewis acid behavior of SF4 : synthesis, characterization, and computational study of adducts of SF4 with pyridine and pyridine derivatives.

Sulfur tetrafluoride was shown to act as a Lewis acid towards organic nitrogen bases, such as pyridine, 2,6-dimethylpyridine, 4-methylpyridine, and 4-dimethylaminopyridine. The SF4 ⋅NC5 H5 , SF4 ⋅2,6-NC5 H3 (CH3 )2 , SF4 ⋅4-NC5 H4 (CH3 ), and SF4 ⋅4-NC5 H4 N(CH3 )2 adducts can be isolated as solids that are stable below -45 °C. The Lewis acid-base adducts were characterized by low-temperature Raman spectroscopy and the vibrational bands were fully assigned with the aid of density functional theory (DFT) calculations. The electronic structures obtained from the DFT calculations were analyzed by the quantum theory of atoms in molecules (QTAIM). The crystal structures of SF4 ⋅NC5 H5 , SF4 ⋅4-NC5 H4 (CH3 ), and SF4 ⋅4-NC5 H4 N(CH3 )2 revealed weak SN dative bonds with nitrogen coordinating in the equatorial position of SF4 . Based on the QTAIM analysis, the non-bonded valence shell charge concentration on sulfur, which represents the lone pair, is only slightly distorted by the weak dative SN bond. No evidence for adducts between quinoline or isoquinoline with SF4 was found by low-temperature Raman spectroscopy.

Spectroscopic characterisation of dimeric oxidation products of phytosterols.

Sterol dimers are the main oxidation products formed during sterols degradation at elevated temperatures. An investigation was carried out to decipher the structure of dimers differing in polarity, formed during ß-sitosterol thermo-oxidation. The oxidation products were fractionated using silica gel into non-polar (NP), mid-polar (MP) and polar fractions (P). Oligomers were further separated by size-exclusion chromatography (SEC). Tentative chemical structures of non-polar, mid-polar and polar dimers were identified using Ag(+)/CIS-MS and APCI-MS procedures after on-line RP-HPLC separation. Further structures were verified by NMR and FT-IR spectroscopies.

Characterization and dynamic properties for the solid inclusion complexes of ß-cyclodextrin and perfluorooctanoic acid.

The structural characterization and dynamic properties of solid-state inclusion complexes (ICs) formed between ß-cyclodextrin (ß-CD; host) and perfluorooctanoic acid (PFOA; guest) were investigated using (13)C NMR spectroscopy. The 1:1 and 2:1 host/guest solid-state complexes were prepared using a modified dissolution method to obtain complexes with high phase purity. These complexes were further characterized using differential scanning calorimetry (DSC), FT-IR spectroscopy, powder X-ray diffraction (PXRD), (19)F directpolarization (DP), and (13)C cross-polarization (CP) with magic-angle spinning (MAS) NMR spectroscopy. The (19)F → (13)C CP results provided unequivocal support for the formation of well-defined inclusion compounds. The phase purity of the complexes formed between ß-CD and PFOA were assessed using the (19)F DP NMR technique at variable temperature (VT) and MAS at 20 kHz. The complexes were found to be of high phase purity when prepared in accordance with the modified dissolution method. The motional dynamics of the guest in the solid complexes were assessed using T1/T2/T1ρ relaxation NMR methods at ambient and VT conditions. The relaxation data revealed reliable and variable guest dynamics for the 1:1 versus 2:1 complexes at the VTs investigated. The motional dynamics of the guest molecules involve an ensemble of axial motions of the whole chain and 120° rotational jumps of the methyl (CF3) group at the termini of the perfluorocarbon chain. The axial and rotational dynamics of the guest in the 1:1 and 2:1 complexes differ in distribution and magnitude in accordance with the binding geometry of the guest within the host.

Characterisation of non-polar dimers formed during thermo-oxidative degradation of ß-sitosterol.

Thermo-oxidative degradation of sterols at temperature typical for frying leads to the formation of oxidised derivatives, fragmented sterols and oligomers. Recent research on sterol oxidation focuses mainly on the oxysterol derivatives formation to the exclusion of compounds with high molecular mass. The aim of this work was to decipher the chemical structure of non-polar dimers formed during ß-sitosterol oxidation at 180°C in the presence of oxygen. The dimer fraction was separated by size-exclusion chromatography (SEC) after pre-fractionation on silica gel. The chemical structure of the dimers was assessed by 1D and 2D NMR, IR, Raman and MS spectroscopies. NMR data confirmed that the predominant non-polar dimer formed during ß-sitosterol oxidative degradation has a configuration of 3ß,3ß'-disitosteryl ether. Data from IR and Raman spectroscopies further proved it chemical structure. Applied analytical techniques also confirmed presence of dimers with different configuration than disteryl ethers.

SF4·N(C2H5)3: the first conclusively characterized SF4 adduct with an organic base.

Sulfur tetrafluoride and triethylamine react at low temperatures to form a 1:1 adduct. The unambiguous characterization of the SF(4)·N(C(2)H(5))(3), which is only stable at low temperature, proves the Lewis acid property of SF(4) towards organic Lewis bases. The S-N bond has a length of 2.384(2) Å and is an archetypical example of a dative S(IV) ← N bonding modality.

Spin-lattice relaxation in aluminum-doped semiconducting 4H and 6H polytypes of silicon carbide.

NMR spin-lattice relaxation efficiency is similar at all carbon and silicon sites in aluminum-doped 4H- and 6H-polytype silicon carbide samples, indicating that the valence band edge (the top of the valence band), where the holes are located in p-doped materials, has similar charge densities at all atomic sites. This is in marked contrast to nitrogen-doped samples of the same polytypes where huge site-specific differences in relaxation efficiency indicate that the conduction band edge (the bottom of the conduction band), where the mobile electrons are located in n-doped materials, has very different charge densities at the different sites. An attempt was made to observe (27)Al NMR signals directly, but they are too broad, due to paramagnetic line broadening, to provide useful information about aluminum doping.

Hydrogen-bonding interactions in T-2 toxin studied using solution and solid-state NMR.

The structure of T-2 toxin in the solid-state is limited to X-ray crystallographic studies, which lack sufficient resolution to provide direct evidence for hydrogen-bonding interactions. Furthermore, its solution-structure, despite extensive Nuclear Magnetic Resonance (NMR) studies, has provided little insight into its hydrogen-bonding behavior, thus far. Hydrogen-bonding interactions are often an important part of biological activity. In order to study these interactions, the structure of T-2 toxin was compared in both the solution- and solid-state using NMR Spectroscopy. It was determined that the solution- and solid-state structure differ dramatically, as indicated by differences in their carbon chemical shifts, these observations are further supported by solution proton spectral parameters and exchange behavior. The slow chemical exchange process and cross-relaxation dynamics with water observed between the hydroxyl hydrogen on C-3 and water supports the existence of a preferential hydrogen bonding interaction on the opposite side of the molecule from the epoxide ring, which is known to be essential for trichothecene toxicity. This result implies that these hydrogen-bonding interactions could play an important role in the biological function of T-2 toxin and posits towards a possible interaction for the trichothecene class of toxins and the ribosome. These findings clearly illustrate the importance of utilizing solid-state NMR for the study of biological compounds, and suggest that a more detailed study of this whole class of toxins, namely trichothecenes, should be pursued using this methodology.

Formation of host-guest complexes of ß-cyclodextrin and perfluorooctanoic acid.

Structural characterization and dynamic properties of solid-state inclusion complexes of ß-cyclodextrin (ß-CD) with perfluorooctanoic acid (PFOA) were investigated by (19)F/(13)C solid-state and (19)F/(1)H solution NMR spectroscopy. The complexes in the solid state were prepared using dissolution and slow cool methods, where thermal analyses (DSC and TGA), PXRD, and FT-IR results provided complementary support that inclusion complexes were formed between ß-CD and PFOA with variable stoichiometry and inclusion geometry. (19)F DP (direct polarization) and (13)C CP (cross-polarization) with magic-angle spinning (MAS) solids NMR, along with (19)F/(1)H solution NMR were used to characterize the complexes in the solid and solution phases, respectively. The dynamics of the guest molecules in the inclusion complexes (ICs) were studied using variable temperature (VT) (19)F DP/MAS NMR experiments in the solid state. The guest molecules were observed to be in several different molecular environments, providing strong evidence of variable host-guest stoichiometry and inclusion geometry, in accordance with the preparation method of the complex and the conformational preference of PFOA. It was concluded from PXRD that ß-CD and PFOA form inclusion complexes with "channel-type" structures. Variable spin rate (VSR) (19)F DP/MAS NMR was used to assess the phase purity of the complexes, and it was revealed that slow cooling resulted in relatively pure phases. In the solution state, (1)H and (19)F NMR complexation-induced chemical shifts (CISs) of ß-CD and PFOA, respectively, provided strong support for the formation of 1:1 and 2:1 ß-CD/PFOA inclusion complexes. The dynamics of the guest molecule in the ß-CD/PFOA complexes in D(2)O solutions were probed using VT (19)F NMR and revealed some guest conformational and exchange dynamics as a function of temperature and the relative concentrations of the host and guest.

Current and future experimental strategies for structural analysis of trichothecene mycotoxins--a prospectus.

Fungal toxins, such as those produced by members of the order Hypocreales, have widespread effects on cereal crops, resulting in yield losses and the potential for severe disease and mortality in humans and livestock. Among the most toxic are the trichothecenes. Trichothecenes have various detrimental effects on eukaryotic cells including an interference with protein production and the disruption of nucleic acid synthesis. However, these toxins can have a wide range of toxicity depending on the system. Major differences in the phytotoxicity and cytotoxicity of these mycotoxins are observed for individual members of the class, and variations in toxicity are observed among different species for each individual compound. Furthermore, while diverse toxicological effects are observed throughout the whole cellular system upon trichothecene exposure, the mechanism of toxicity is not well understood. In order to comprehend how these toxins interact with the cell, we must first have an advanced understanding of their structure and dynamics. The structural analysis of trichothecenes was a subject of major interest in the 1980s, and primarily focused on crystallographic and solution-state Nuclear Magnetic Resonance (NMR) spectroscopic studies. Recent advances in structural determination through solution- and solid-state NMR, as well as computation based molecular modeling is leading to a resurgent interest in the structure of these and other mycotoxins, with the focus shifting in the direction of structural dynamics. The purpose of this work is to first provide a brief overview of the structural data available on trichothecenes and a characterization of the methods commonly employed to obtain such information. A summary of the current understanding of the relationship between structure and known function of these compounds is also presented. Finally, a prospectus on the application of new emerging structural methods on these and other related systems is discussed.